1. Field of the Invention
The present invention relates to a five-port switching valve with residual pressure exhaust valve including a five-port electromagnetic switching valve and a residual pressure exhaust valve that automatically discharges residual pressure remaining in a fluid pressure circuit to and from which pressure air is supplied and discharged via the switching valve, the residual pressure exhaust valve constituting a safety circuit that prevents malfunction or unexpected behavior of the fluid pressure apparatus due to the residual pressure.
2. Description of the Related Art
In a general-purpose five-port electromagnetic switching valve of a closed-center type includes, for example, a valve cavity penetrating through the main valve body. A central supply flow path, a pair of output flow paths located on the respective sides of the central supply flow path, and a pair of discharge flow paths located on the side of the respective end portions of the valve cavity from the respective discharge flow paths, each have an opening in the valve cavity. The supply flow path is disposed to communicate with a supply port having an opening on the outer face of the main valve body, and the output flow paths on the respective sides of the supply flow path are disposed to respectively communicate with a pair of output ports of the main valve body, and further the discharge flow paths located beside the respective output flow paths are disposed to respectively communicate with a pair of discharge ports of the main valve body.
A main valve element, with an annular seal member formed of an elastic material attached therearound, is slidably fitted inside the valve cavity, and the main valve element is driven with fluid pressure operational force exerted on one of pistons to be made to abut the respective end portions of the main valve element, so as to set the main valve element valve cavity at one of two switching positions. One is a first switching position in which the supply port is set to communicate with one of the output ports and the other output port is set to communicate with the discharge port, and a second switching position in which, contrary to the above, the supply port is set to communicate with the other output port and the first mentioned output port is set to communicate with the discharge port. The main valve element can also be set to a neutral position in which all of the flow paths in the valve cavity are restricted from communicating with any other flow paths by biasing force of a spring exerted on the main valve element, in the case where the fluid pressure operational force is not exerted on any of the pistons.
In the five-port switching valve settable to the closed-center position (neutral position), fluid pressure is supplied from the supply port to one of the output ports so as to operate a fluid pressure apparatus connected to the output port. When the main valve element is reset to the neutral position to stop the operation of the fluid pressure apparatus, the pressure air which has thus far been operating the fluid pressure apparatus through the five-port switching valve is enclosed as residual pressure on the side of the fluid pressure circuit. In case that the residual pressure is discharged owing to an unexpected situation, the fluid pressure apparatus in which the residual pressure has been enclosed may malfunction or make an unexpected behavior thus incurring a dangerous situation, and therefore the residual pressure has to be discharged in advance in order to avoid such danger.